In an era of bilateral funding and changing criteria, when is unilateral cochlear implantation a better option?

BACKGROUND: Funding for paediatric bilateral cochlear implantation became available in Ireland in 2014. Prior to this, children eligible for cochlear implantation received a unilateral implant. OBJECTIVE: To examine the cohort of children who received a unilateral cochlear implant in the 4 year period following bilateral cochlear implantation funding becoming available. METHODS: A clinical audit of all children implanted for the first time between July 2014 and July 2018. The unilaterally implanted children (n = 105) were divided into 3 groups according to whether they met the audiometric thresholds for implantation in neither ear (Group 1), one ear (Group 2) or both ears (Group 3). One year post operative functional outcomes were examined for all 3 groups. RESULTS: All 3 groups showed significant improvements in functional outcomes at 1 year post op. To date, 20% of the unilaterally implanted children have proceeded to get a sequential CI, often where there was no change in audiological status. CONCLUSIONS: The number of children in Groups 1 and 2 highlighted how our decision making around cochlear implantation has changed in recent years. Unilateral cochlear implantation in certain circumstances is good practice, independent of the audiological profile when an experienced multi-disciplinary team (MDT) is involved in the decision making process. Decision making using a holistic model approach is key, including involving the parent/carer and, where appropriate, the child/teenager themselves. A staged bilateral cochlear implant is also a good option, where careful monitoring and support for the first implant has resulted in positive outcomes.

Objective assessment of spectral ripple discrimination in cochlear implant listeners using cortical evoked responses to an oddball paradigm.

Cochlear implants (CIs) can partially restore functional hearing in deaf individuals. However, multiple factors affect CI listener's speech perception, resulting in large performance differences. Non-speech based tests, such as spectral ripple discrimination, measure acoustic processing capabilities that are highly correlated with speech perception. Currently spectral ripple discrimination is measured using standard psychoacoustic methods, which require attentive listening and active response that can be difficult or even impossible in special patient populations. Here, a completely objective cortical evoked potential based method is developed and validated to assess spectral ripple discrimination in CI listeners. In 19 CI listeners, using an oddball paradigm, cortical evoked potential responses to standard and inverted spectrally rippled stimuli were measured. In the same subjects, psychoacoustic spectral ripple discrimination thresholds were also measured. A neural discrimination threshold was determined by systematically increasing the number of ripples per octave and determining the point at which there was no longer a significant difference between the evoked potential response to the standard and inverted stimuli. A correlation was found between the neural and the psychoacoustic discrimination thresholds (R2=0.60, p<0.01). This method can objectively assess CI spectral resolution performance, providing a potential tool for the evaluation and follow-up of CI listeners who have difficulty performing psychoacoustic tests, such as pediatric or new users.

Auditory mismatch negativity in cochlear implant users: a window to spectral discrimination.

A cochlear implant (CI) can partially restore hearing in patients with severe to profound sensorineural hearing loss. However, the large outcome variability in CI users prompts the need for more objective measures of speech perception performance. Electrophysiological metrics of CI performance may be an important tool for audiologists in the assessment of hearing rehabilitation. Utilizing electroencephalography (EEG), it may be possible to evaluate speech perception correlates such as spectral discrimination. The mismatch negativity (MMN) of 10 CI subjects was recorded for stimuli containing different spectral densities. The neural spectral discrimination threshold, estimated by the MMN responses, showed a significant correlation with the behavioral spectral discrimination threshold measured in each subject. Results suggest that the MMN can be potentially used to obtain an objective estimate of spectral discrimination abilities in CI users.